This invention relates to the treatment of "sour" petroleum and coal liquefaction oils containing hydrogen sulfide and other organosulfur compounds such as thiols and thiocarboxylic acids, and more particularly, to improved methods of treating such streams.
Petroleum and synthetic coal liquefaction crude oils are converted into finished products in a fuel products refinery, where principally the products are motor gasoline, distillate fuels (diesel and heating oils), and bunker (residual) fuel oil. Atmospheric and vacuum distillation towers separate the crude into narrow boiling fractions. The vacuum tower cuts deeply into the crude while avoiding temperatures above about 800.degree. F. which cause thermal cracking. A catalytic cracking unit cracks high boiling vacuum gas oil into a mixture from light gases to very heavy tars and coke. In general, very heavy virgin residuum (average boiling points greater than 1100.degree. F.) is blended into residual fuel oil or thermally cracked into lighter products in a visbreaker or coker.
Overhead or distillate products in the refining process generally contain very little, if any, hydrogen sulfide, but may contain sulfur components found in the crude oil, including mercaptans and organosulfides. However, substantial amounts of hydrogen sulfide, as well as mercaptans and organosulfides, are found in vacuum distillation tower bottoms, which may be blended into gas oils and fuel oils.
As employed in this application, "oil" is meant to include the unrefined and refined hydrocarbonaceous products derived from petroleum or from liquefaction of coal, both of which contain sulfur compounds. Thus, the term "oil" includes, particularly for petroleum based fuels, wellhead condensate as well as crude oil which may be contained in storage facilities at the producing field and transported from those facilities by barges, pipelines, tankers, or trucks to refinery storage tanks, or, alternatively, may be transported directly from the producing facilities through pipelines to the refinery storage tanks. The term "oil" also includes refined products, interim and final, produced in a refinery, including distillates such as gasolines, distillate fuels, fuel products, oils, and residual fuels.
Hydrogen sulfide which collects in vapor spaces above confined hydrogen sulfide containing oils (for example, in storage tanks or barges) is poisonous, in sufficient quantities, to workers exposed to the hydrogen sulfide. Refined fuels must be brought within sulfide and mercaptan specifications for marketability. In the processing of oils, it is desirable to eliminate or reduce atmospheric emissions of noxious hydrogen sulfide, mercaptan or other sulfhydryl compounds associated with sulfur containing oils, in order to improve environmental air quality at refineries.
Oils have been treated with caustic soda and chemicals to reduce hydrogen sulfide content. Because it is relatively inexpensive, caustic soda (sodium hydroxide) is commonly used to treat, up to a maximum sodium limit, the bunker fuels which principally are burned by utilities or ships. Excess sodium in bunker fuels forms inorganic products that cause undesirable ash, plugged burner tips and boiler slagging. Chemical treatments are necessary to further reduce H.sub.2 S content of bunker fuels which have a sodium content at maximum limits.
Some distillates and fuel products such as gas oils and aviation fuels cannot be treated with caustic. Gas oils are a fuel intermediate fed to fluid catalatic crackers, and sodium poisons the catalysts in the catalytic crackers. Aviation fuel cannot be treated with caustic because the sodium gives inorganic products that foul engines. Asphalt products can't be treated with caustic because the caustic changes the physical properties of the product, for example, increasing the softening point. These oils are a fuel product of commerce bought and sold among refineries and transported by barge. Barge operators dislike transporting oil which has more than a minimal H.sub.2 S content, because H.sub.2 S vapor escaping from the fuel is life threatening. Treatment is necessary to reduce H.sub.2 S to acceptable limits.
The prior art relating to the treatment of sour petroleum oils includes methods in which choline base has been employed to treat sour heavy fuel oils to maintain the hydrogen sulfide content in the atmosphere above or associated with such oils at levels within acceptable limits to avoid health hazards to personnel, as disclosed in U.S. Pat. No. 4,867,865. Choline base also has been used to treat gasoline and other motor fuels to remove organosulfur compounds such as thiols, thiolcarboxylic acids, disulfides and polysulfides, as disclosed in U.S. Pat. No. 4,594,147.
The use of choline base for these purposes is effective, but we have discovered a more effective treatment to reduce hazards of hydrogen sulfide exposure to workers, to bring fuels within hydrogen sulfide or mercaptan specifications, and to eliminate or reduce atmospheric emissions of noxious hydrogen sulfide, mercaptan or other sulfhydryl compound odors associated with such fuels for improved environmental air quality.